1. Field of the Invention
This invention concerns memory devices for propagating domains in thin polycrystalline ferromagnetic layers having uniaxial anisotropy, deposited on an insulating substrate and more particularly an arrangement for facilitating domain propagation.
2. Description of the Prior Art
In a magnetic domain propagation register, propagation is effected in a "soft" magnetic zone having slight coercivity, with a suitable shape, surrounded by a magnetic zone having greater coercivity, under the control of a clock.
Co-pending U.S. application Ser. No. 372,866 filed on June 6, 1973, now U.S. Pat. No. 3,889,246, describes a register whose operation is identical to that of this application, for propagating magnetic domains in a zone formed by a magnetic layer having uniaxial anisotropy with slight coercivity, or soft zone, surrounded by a zone having greater coercivity, or hard zone, that register being of the type forming several parallel segments each of which comprises a central zone and, on each side, a lateral zone having divisions with edges which are alternately straight or inclined in relation to the axis of the central zone and comprising, in a functional combination:
1. A conductor, called the lateral conductor, in a Greek border configuration of sinuous form having several legs each of which covers alternately the divisions on one side and the divisions of the other side of the central zone and, possibly, the divisions on the opposite side of the adjacent segment having slight coercivity, that material conductor ensuring simultaneously the growth of the domains beneath one leg and the deleting of the domains beneath the adjacent leg;
2. A central conductor, in a Greek border configuration of sinuous form, having a width approximately equivalent to the said space between two legs of the lateral conductor, for example greater or smaller by 0 to 40%, in which one every other leg covers a central part of the segment or of the central parts of several segments, that control conductor ensuring the transfer of the domains from the divisions which are beneath one leg of the lateral conductor to the divisions which are beneath the adjacent leg.
In such a register, a system having two conductors is therefore sufficient to ensure the propagation of the domains in a thin magnetic layer structure in which zones having a low coercitive field in the shape of teeth having an oblique slope, which are asymetrical, channel the unilateral direction of movement of the domains. The conductor on the first level, called the central conductor, enables, when a current of one polarity crosses through it, the growth of the domains in the central zone of the propagation channels, in the soft layer.
The conductor on the second level, called the lateral conductor, is crossed by pulses of bipolar current which enable, simultaneously, the growth of a domain in a top finger of the channel and the deleting of the other end of the same domain in a bottom finger of the channel. The data is kept in the form of a domain whose magnetization is anti-parallel to the general reset to zero direction of the magnetization, itself parallel to the easy axis of the soft magnetic layer. The uniaxial anisotropy is induced at the time of the depositing by a 50-Oersted magnetic field.
The data bearing domain is kept in a finger of the channel and its size is greater than the critical size beneath which a domain is spontaneously deleted, mainly under the effect of the demagnetizing field set up by the magnetic charges of opposite sign existing at the two points of the domain. More particularly, for a soft layer of coercitive field equal to 3 Oersteds, domains of 10 .mu. .times. 100 .mu. will be stable.
The preserving of smaller domains would be possible if an outside field were maintained in the direction of the magnetization of the domain, for example, an outside field of 2 Oersteds would enable the preserving of a 5 .mu. .times. 30 .mu. domain and therefore the increasing of the density of storage by a large factor.